In which of the following arrangements is the order $NOT$ according to the property indicated against it?

Explain the following:
$(a)$ Electronegativity of elements increases on moving from left to right in the periodic table.
$(b)$ Ionisation enthalpy decreases in a group from top to bottom.

Fill in the blanks given below:
$(i)$ The most widely used scale for measuring electronegativity is ........ .
$(ii)$ The similarity observed in periodic properties is known as .............. .
$(iii)$ The elements located in the middle of the periodic table form .......... type of oxides.

What is the basic difference between the terms electron gain enthalpy and electronegativity?

Given below are two statements $:$
Statement $(I) :$ The radii of isoelectronic species increase in the order $Mg^{2+} < Na^{+} < F^{-} < O^{2-}$.
Statement $(II) :$ The magnitude of electron gain enthalpy of halogens decreases in the order $Cl > F > Br > I$.
In the light of the above statements,choose the most appropriate answer from the options given below $:$

Consider the following orders :-
$(I)$ $Li > Na$ (Reducing nature)
$(II)$ $BF_3 > BCl_3 > BBr_3 > BI_3$ (Rate of hydrolysis)
$(III)$ $B > C > N > O > F$ ($1^{st}$ ionization energy)
$(IV)$ $CCl_4 > SiCl_4$ (Boiling point)
The $CORRECT$ order$(s)$ are :-